AT&T’s 3G Speeds

I am finding AT&T’s 3G speeds to be very hit and miss so far on my iPad 3G. For example the first two speed tests that I did this morning in Detroit showed 104 kbps and 93 Kbps down then a third hit 500 Kbps. The first two tests are essentially Edge speeds, the last is more like what I should see all the time.